feat(marketplace): mutual trade attestations + reputation (kind 31871)

Built on the Attestations NIP (31871); a listing is the Assertion Event:
- Seller 'Mark as sold' now opens a dialog (buyer npub + self-reported method +
  optional amount) that marks the listing sold AND publishes a trade attestation
- Buyer sees 'Confirm this trade' on the listing and publishes the mirror
  attestation -> mutual pair = a verified trade
- useTradeReputation aggregates sales/purchases/verified + counterparties
- Profile 'Trades' card; seller 'N verified trades' badge on listing cards
- NIP.md documents kind 31871 usage + our p/method/amount extensions
Payment method is self-reported metadata, never proof of payment.

NIP.md

@@ -3070,3 +3070,73 @@ and laptop.
   seconds and flushes on `pagehide`/`beforeunload`, so relays are never spammed.
 - **Anon users.** With no signer (or no NIP-44), sync is a no-op and behavior is
   identical to the previous localStorage-only implementation.
+
+---
+
+# Trade Attestations (kind 31871)
+
+Marketplace reputation is built on the **Attestations** NIP
+(<https://nostr.com/naddr1qvzqqqrcvypzp384u7n44r8rdq74988lqcmggww998jjg0rtzfd6dpufrxy9djk8qy28wumn8ghj7un9d3shjtnyv9kh2uewd9hsqrrpw36x2um5v96xjmmwwvuhdk8z>),
+authored by `npub1cn670f663n3ks02jnnlsvd5y88zjnefy8343ykaxs7y3nzzketrsrjwt8a`.
+
+A **listing** (kind `30402`) is the *Assertion Event*. When a deal closes, both
+parties can publish a `31871` Attestation about it. Two reciprocal attestations
+on the same listing form a **verified trade**.
+
+## Seller — sale completed
+
+```json
+{
+  "kind": 31871,
+  "tags": [
+    ["d", "<seller_pubkey>:trade:sold:<listing-d>"],
+    ["a", "30402:<seller>:<listing-d>"],
+    ["s", "valid"],
+    ["p", "<buyer_pubkey>"],
+    ["method", "cash|lightning|trade|other"],
+    ["amount", "45000", "SATS"],
+    ["alt", "SkateSpots: sale completed"]
+  ],
+  "content": "Sold to @buyer. Paid in cash."
+}
+```
+
+## Buyer — purchase confirmed
+
+Same shape, `d` ends `:trade:bought:<listing-d>`, `p` names the **seller**, and
+`content` is a human description.
+
+## Extension tags (SkateSpots profile)
+
+The base NIP has no counterparty field for this use case, so we add:
+
+| Tag | Meaning |
+| --- | --- |
+| `p` | The **other party** in the trade (required by us, marks a trade attestation) |
+| `method` | Self-reported payment method: `cash`, `lightning`, `trade`, `other` |
+| `amount` | Optional self-reported amount, `["amount","45000","SATS"]` |
+
+`method`/`amount` are **self-reported metadata, never proof of payment** — the app
+cannot observe off-app (cash/trade) settlement.
+
+## States & revocation
+
+`["s", "verifying" | "valid" | "revoked"]` follows the NIP's lifecycle. Because
+`31871` is addressable, re-publishing the same `d` with `["s","revoked"]`
+retracts an attestation (e.g. a disputed or cancelled deal).
+
+## Reputation semantics
+
+- **sales** — listings where the attestor is the listing author
+- **purchases** — listings where the attestor is not the author
+- **verified** — seller **and** counterparty both attested the same listing
+- Consumers **trust-weight counterparties** with the existing web-of-trust score
+  (as with Scene vouches) so fresh-account rings cannot inflate reputation.
+
+## Future (from the NIP)
+
+- `31872` **Attestation Request** — a buyer can request the seller's attestation;
+  it carries a `cashu_token` lockable to spending conditions (HTLC/P2PK) → a
+  Cashu-based escrow / release-on-attestation flow.
+- `31873` **Attestor Recommendation** / `11871` **Proficiency** — trusted-trader
+  endorsements and attestor discovery.

src/components/MarkSoldDialog.tsx

@@ -0,0 +1,169 @@
+import { useState } from 'react';
+import { nip19 } from 'nostr-tools';
+import {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogHeader,
+  DialogTitle,
+} from '@/components/ui/dialog';
+import { Button } from '@/components/ui/button';
+import { Input } from '@/components/ui/input';
+import { Label } from '@/components/ui/label';
+import { useTradeAttestation, TRADE_METHODS, type TradeMethod } from '@/hooks/useTradeAttestations';
+import { useMarkListingSold } from '@/hooks/useMarkListingSold';
+import { useToast } from '@/hooks/useToast';
+import { cn } from '@/lib/utils';
+import { Check, Loader2 } from 'lucide-react';
+import type { NostrEvent } from '@nostrify/nostrify';
+
+function resolvePubkey(input: string): string | null {
+  const t = input.trim();
+  if (/^[a-f0-9]{64}$/i.test(t)) return t.toLowerCase();
+  if (t.startsWith('npub1')) {
+    try {
+      const decoded = nip19.decode(t);
+      return decoded.type === 'npub' ? decoded.data : null;
+    } catch {
+      return null;
+    }
+  }
+  return null;
+}
+
+/**
+ * Seller's "close the deal" flow: mark the listing sold AND publish a trade
+ * attestation (kind 31871) naming the buyer, so both sides can build
+ * reputation. Payment method is self-reported — the app can't see cash/trade
+ * deals and never treats it as proof of payment.
+ */
+export function MarkSoldDialog({
+  open,
+  onOpenChange,
+  event,
+  listing,
+}: {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+  event: NostrEvent;
+  listing: { pubkey: string; identifier: string };
+}) {
+  const { publishTrade, isPending: publishing } = useTradeAttestation();
+  const { markSold, isPending: marking } = useMarkListingSold();
+  const { toast } = useToast();
+
+  const [buyer, setBuyer] = useState('');
+  const [method, setMethod] = useState<TradeMethod>('cash');
+  const [amount, setAmount] = useState('');
+
+  const buyerPubkey = resolvePubkey(buyer);
+  const busy = publishing || marking;
+
+  const submit = async () => {
+    if (!buyerPubkey) {
+      toast({ title: 'Enter the buyer’s npub', variant: 'destructive' });
+      return;
+    }
+    try {
+      await markSold(event);
+      await publishTrade({
+        listing,
+        role: 'sold',
+        counterparty: buyerPubkey,
+        method,
+        amountSats: amount.trim() ? Number(amount) : undefined,
+      });
+      toast({
+        title: 'Deal closed 🎉',
+        description: 'Listing marked sold and the trade was published for reputation.',
+      });
+      onOpenChange(false);
+      setBuyer('');
+      setAmount('');
+    } catch (e) {
+      toast({
+        title: 'Could not close the deal',
+        description: e instanceof Error ? e.message : 'Something went wrong.',
+        variant: 'destructive',
+      });
+    }
+  };
+
+  return (
+    <Dialog open={open} onOpenChange={onOpenChange}>
+      <DialogContent className="mx-4 max-w-[calc(100vw-2rem)] border-2 border-[#ccff00]/40 bg-black sm:max-w-md">
+        <DialogHeader>
+          <DialogTitle className="text-white">Close the deal</DialogTitle>
+          <DialogDescription className="text-sm text-gray-400">
+            Marks this listing sold and records a signed trade attestation for you and the buyer.
+          </DialogDescription>
+        </DialogHeader>
+
+        <div className="space-y-4">
+          <div className="space-y-2">
+            <Label htmlFor="buyer" className="flex items-center gap-2 text-xs uppercase tracking-wide text-gray-400">
+              Buyer&apos;s npub
+              {buyerPubkey && <Check className="h-3.5 w-3.5 text-[#ccff00]" />}
+            </Label>
+            <Input
+              id="buyer"
+              value={buyer}
+              onChange={(e) => setBuyer(e.target.value)}
+              placeholder="npub1…"
+              className="h-11 border-gray-700 bg-gray-900 font-mono text-xs text-white"
+            />
+          </div>
+
+          <div className="space-y-2">
+            <Label className="text-xs uppercase tracking-wide text-gray-400">How was it paid? (self-reported)</Label>
+            <div className="flex flex-wrap gap-2">
+              {(Object.keys(TRADE_METHODS) as TradeMethod[]).map((m) => (
+                <button
+                  key={m}
+                  type="button"
+                  onClick={() => setMethod(m)}
+                  className={cn(
+                    'rounded-full border px-3 py-1.5 text-xs font-bold transition-colors',
+                    method === m
+                      ? 'border-[#ccff00] bg-[#ccff00]/15 text-[#ccff00]'
+                      : 'border-white/15 text-gray-400 hover:border-white/30',
+                  )}
+                >
+                  {TRADE_METHODS[m]}
+                </button>
+              ))}
+            </div>
+          </div>
+
+          <div className="space-y-2">
+            <Label htmlFor="amount" className="text-xs uppercase tracking-wide text-gray-400">
+              Amount in sats (optional)
+            </Label>
+            <Input
+              id="amount"
+              value={amount}
+              onChange={(e) => setAmount(e.target.value)}
+              inputMode="numeric"
+              placeholder="e.g. 45000"
+              className="h-11 border-gray-700 bg-gray-900 text-white"
+            />
+          </div>
+
+          <div className="flex gap-2 pt-1">
+            <Button variant="outline" onClick={() => onOpenChange(false)} className="flex-1 border-white/15">
+              Cancel
+            </Button>
+            <Button
+              onClick={submit}
+              disabled={busy || !buyerPubkey}
+              className="flex-1 gap-2 bg-[#ccff00] font-bold text-black hover:bg-[#ccff00]/90"
+            >
+              {busy ? <Loader2 className="h-4 w-4 animate-spin" /> : <Check className="h-4 w-4" />}
+              Mark sold
+            </Button>
+          </div>
+        </div>
+      </DialogContent>
+    </Dialog>
+  );
+}

src/components/MarketplaceItemCard.tsx

@@ -32,6 +32,8 @@ import { useListingReports } from '@/hooks/useListingReports';
 import { useSellerInfo } from '@/hooks/useSellerInfo';
 import { useTrustScore } from '@/hooks/useTrustScore';
 import { useMarkListingSold } from '@/hooks/useMarkListingSold';
+import { MarkSoldDialog } from '@/components/MarkSoldDialog';
+import { useListingTrade, useTradeAttestation, useTradeReputation } from '@/hooks/useTradeAttestations';
 import { DeleteEntityDialog } from '@/components/DeleteEntityDialog';
 import { genUserName } from '@/lib/genUserName';
 import { TrustBadge } from '@/components/TrustBadge';
@@ -66,7 +68,7 @@ export function MarketplaceItemCard({ item, compact = false }: MarketplaceItemCa
   const { toast } = useToast();
   const navigate = useNavigate();
   const { mutateAsync: publishEvent } = useNostrPublish();
-  const { markSold, relist, isPending: isUpdatingStatus } = useMarkListingSold();
+  const { relist, isPending: isUpdatingStatus } = useMarkListingSold();
   const author = useAuthor(item.pubkey);
   const metadata = author.data?.metadata;
   const displayName = metadata?.name ?? genUserName(item.pubkey);
@@ -88,6 +90,13 @@ export function MarketplaceItemCard({ item, compact = false }: MarketplaceItemCa
   const [reportReason, setReportReason] = useState<string>('');
   const [reportDetails, setReportDetails] = useState('');
   const [isReporting, setIsReporting] = useState(false);
+  const [showMarkSold, setShowMarkSold] = useState(false);
+
+  // Trade attestations (Attestations NIP, kind 31871) — see useTradeAttestations.
+  const listingRef = { pubkey: item.pubkey, identifier: item.identifier };
+  const { data: trade } = useListingTrade(listingRef, user?.pubkey);
+  const { data: sellerRep } = useTradeReputation(item.pubkey);
+  const { publishTrade, isPending: confirmingTrade } = useTradeAttestation();
 
   // Format price display
   const priceDisplay = item.price
@@ -182,14 +191,25 @@ export function MarketplaceItemCard({ item, compact = false }: MarketplaceItemCa
   const isOwnListing = user?.pubkey === item.pubkey;
   const isSold = item.status === 'sold';
 
-  const handleMarkSold = async () => {
+  // Was the viewer named as the buyer by the seller? Then they can confirm.
+  const sellerNamedMe =
+    !!user &&
+    !isOwnListing &&
+    !!trade &&
+    trade.attestations.some(
+      (ev) => ev.pubkey === item.pubkey && ev.tags.some(([t, v]) => t === 'p' && v === user.pubkey),
+    );
+  const iConfirmedTrade = !!trade?.iConfirmed;
+
+  const handleConfirmTrade = async () => {
+    if (!user) return;
     try {
-      await markSold(item.event);
-      toast({ title: 'Marked as sold', description: 'Your listing is now shown as sold.' });
-    } catch (error) {
+      await publishTrade({ listing: listingRef, role: 'bought', counterparty: item.pubkey });
+      toast({ title: 'Trade confirmed', description: 'Reputation updated for both of you.' });
+    } catch (e) {
       toast({
-        title: 'Could not update',
-        description: error instanceof Error ? error.message : 'Something went wrong',
+        title: 'Could not confirm the trade',
+        description: e instanceof Error ? e.message : 'Something went wrong.',
         variant: 'destructive',
       });
     }
@@ -332,7 +352,7 @@ export function MarketplaceItemCard({ item, compact = false }: MarketplaceItemCa
                           Relist as active
                         </DropdownMenuItem>
                       ) : (
-                        <DropdownMenuItem onClick={handleMarkSold} disabled={isUpdatingStatus}>
+                        <DropdownMenuItem onClick={() => setShowMarkSold(true)} disabled={isUpdatingStatus}>
                           <CheckCircle className="h-4 w-4 mr-2" />
                           Mark as sold
                         </DropdownMenuItem>
@@ -369,6 +389,12 @@ export function MarketplaceItemCard({ item, compact = false }: MarketplaceItemCa
                   {categoryLabel}
                 </Badge>
               )}
+              {sellerRep && sellerRep.verified > 0 && (
+                <Badge variant="outline" className="text-xs border-[#ccff00]/40 bg-[#ccff00]/10 text-[#ccff00]">
+                  <CheckCircle className="h-3 w-3 mr-1" />
+                  {sellerRep.verified} verified trade{sellerRep.verified === 1 ? '' : 's'}
+                </Badge>
+              )}
             </div>
 
             {/* Description */}
@@ -461,6 +487,19 @@ export function MarketplaceItemCard({ item, compact = false }: MarketplaceItemCa
                   "coming soon" toast is a dead end — buyers contact the seller
                   and arrange payment directly. */}
 
+              {/* Buyer: confirm the trade the seller recorded (builds both reps) */}
+              {sellerNamedMe && !iConfirmedTrade && (
+                <Button
+                  size="sm"
+                  onClick={handleConfirmTrade}
+                  disabled={confirmingTrade}
+                  className="w-full gap-2 bg-[#ccff00] font-bold text-black hover:bg-[#ccff00]/90"
+                >
+                  {confirmingTrade ? <Loader2 className="h-4 w-4 animate-spin" /> : <CheckCircle className="h-4 w-4" />}
+                  Confirm this trade
+                </Button>
+              )}
+
               {/* Contact button */}
               <Button
                 variant="outline"
@@ -480,6 +519,16 @@ export function MarketplaceItemCard({ item, compact = false }: MarketplaceItemCa
         </div>
       </CardContent>
 
+      {/* Seller: close the deal (mark sold + publish trade attestation) */}
+      {isOwnListing && (
+        <MarkSoldDialog
+          open={showMarkSold}
+          onOpenChange={setShowMarkSold}
+          event={item.event}
+          listing={listingRef}
+        />
+      )}
+
       {/* Delete confirmation (controlled — trigger lives in the owner dropdown) */}
       <DeleteEntityDialog
         event={item.event}

src/components/TradeReputationCard.tsx

@@ -0,0 +1,52 @@
+import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
+import { useTradeReputation } from '@/hooks/useTradeAttestations';
+import { cn } from '@/lib/utils';
+import { Handshake } from 'lucide-react';
+
+function Stat({ label, value, accent }: { label: string; value: number; accent?: boolean }) {
+  return (
+    <div className="rounded-lg border border-white/10 bg-white/[0.03] px-2 py-3">
+      <p className={cn('text-xl font-black', accent ? 'text-[#ccff00]' : 'text-white')}>{value}</p>
+      <p className="text-[10px] uppercase tracking-wide text-gray-500">{label}</p>
+    </div>
+  );
+}
+
+/**
+ * Marketplace reputation for a profile, derived from mutually-signed trade
+ * attestations (kind 31871, see NIP.md → Trade Attestations).
+ *
+ * "Verified" is the strong signal: the seller AND the counterparty both signed
+ * an attestation for the same listing. Renders nothing when there are no trades.
+ */
+export function TradeReputationCard({ pubkey, className }: { pubkey: string; className?: string }) {
+  const { data } = useTradeReputation(pubkey);
+  const total = (data?.sales ?? 0) + (data?.purchases ?? 0);
+
+  if (!data || total === 0) return null;
+
+  return (
+    <Card className={cn('bg-black/90 border-2 border-[#ff6600]/25', className)}>
+      <CardHeader className="pb-3">
+        <CardTitle className="flex items-center gap-2 text-lg text-[#ff6600]">
+          <Handshake className="h-5 w-5" />
+          Trades
+        </CardTitle>
+      </CardHeader>
+      <CardContent className="space-y-3">
+        <div className="grid grid-cols-3 gap-2 text-center">
+          <Stat label="Verified" value={data.verified} accent />
+          <Stat label="Sales" value={data.sales} />
+          <Stat label="Purchases" value={data.purchases} />
+        </div>
+        <p className="text-xs text-gray-500">
+          {data.verified > 0
+            ? `${data.verified} mutually-confirmed ${data.verified === 1 ? 'trade' : 'trades'}`
+            : 'Awaiting mutual confirmation'}
+          {data.counterparties.length > 0 &&
+            ` · ${data.counterparties.length} counterpart${data.counterparties.length === 1 ? 'y' : 'ies'}`}
+        </p>
+      </CardContent>
+    </Card>
+  );
+}

src/hooks/useTradeAttestations.test.ts

@@ -0,0 +1,58 @@
+import { describe, it, expect } from 'vitest';
+import type { NostrEvent } from '@nostrify/nostrify';
+import { parseListingCoord, isTradeAttestation, TRADE_ATTESTATION_KIND } from './useTradeAttestations';
+
+function ev(partial: Partial<NostrEvent> & Pick<NostrEvent, 'kind' | 'pubkey' | 'id'>): NostrEvent {
+  return { content: '', created_at: 0, sig: '', tags: [], ...partial } as NostrEvent;
+}
+
+describe('parseListingCoord', () => {
+  it('parses a 30402 coordinate', () => {
+    expect(parseListingCoord('30402:abc123:my-listing')).toEqual({
+      kind: 30402,
+      pubkey: 'abc123',
+      identifier: 'my-listing',
+    });
+  });
+
+  it('keeps colons that are part of the identifier', () => {
+    expect(parseListingCoord('30402:abc123:slug:part2')?.identifier).toBe('slug:part2');
+  });
+
+  it('returns null for missing or malformed coords', () => {
+    expect(parseListingCoord(undefined)).toBeNull();
+    expect(parseListingCoord('nope')).toBeNull();
+    expect(parseListingCoord('30402:onlypubkey')).toBeNull();
+  });
+});
+
+describe('isTradeAttestation', () => {
+  it('accepts a 31871 attestation of a 30402 listing with a counterparty', () => {
+    const e = ev({
+      kind: TRADE_ATTESTATION_KIND,
+      pubkey: 'seller',
+      id: 'a1',
+      tags: [['a', '30402:seller:deck'], ['p', 'buyer'], ['s', 'valid']],
+    });
+    expect(isTradeAttestation(e)).toBe(true);
+  });
+
+  it('rejects an attestation without a counterparty', () => {
+    const e = ev({
+      kind: TRADE_ATTESTATION_KIND,
+      pubkey: 'x',
+      id: 'a2',
+      tags: [['a', '30402:x:y'], ['s', 'valid']],
+    });
+    expect(isTradeAttestation(e)).toBe(false);
+  });
+
+  it('rejects non-listing assertions and other kinds', () => {
+    expect(
+      isTradeAttestation(ev({ kind: TRADE_ATTESTATION_KIND, pubkey: 'x', id: 'a3', tags: [['a', '35000:x:y'], ['p', 'z']] })),
+    ).toBe(false);
+    expect(
+      isTradeAttestation(ev({ kind: 1, pubkey: 'x', id: 'a4', tags: [['a', '30402:x:y'], ['p', 'z']] })),
+    ).toBe(false);
+  });
+});

src/hooks/useTradeAttestations.ts

@@ -0,0 +1,252 @@
+import { useQuery } from '@tanstack/react-query';
+import { useNostr } from '@nostrify/react';
+import type { NostrEvent } from '@nostrify/nostrify';
+import { useNostrPublish } from '@/hooks/useNostrPublish';
+import { useCurrentUser } from '@/hooks/useCurrentUser';
+import { MARKETPLACE_ITEM_KIND } from '@/lib/types';
+
+/**
+ * Trade attestations (completed deals) — built on the Attestations NIP
+ * (kind 31871), see NIP.md → "Trade Attestations".
+ *
+ * A **listing** (kind 30402) is the *Assertion Event*. When a deal closes:
+ *   • the seller publishes a `31871` attesting it (`s=valid`) and naming the
+ *     buyer in a `p` tag (our documented extension);
+ *   • the buyer may publish a mirror `31871` naming the seller.
+ * Two reciprocal attestations on the same listing = a **verified trade**.
+ *
+ * Payment method is self-reported metadata; the app cannot observe cash/trade
+ * deals and never treats these as proof of payment.
+ */
+export const TRADE_ATTESTATION_KIND = 31871;
+
+export const TRADE_METHODS = {
+  cash: 'Cash',
+  lightning: 'Lightning',
+  trade: 'Trade',
+  other: 'Other',
+} as const;
+
+export type TradeMethod = keyof typeof TRADE_METHODS;
+export type TradeRole = 'sold' | 'bought';
+
+export interface ListingCoord {
+  kind: number;
+  pubkey: string;
+  identifier: string;
+}
+
+/** Parse an `a` tag ("30402:<pubkey>:<d>") into its parts, or null. */
+export function parseListingCoord(aTag: string | undefined): ListingCoord | null {
+  if (!aTag) return null;
+  const [kindStr, pubkey, ...rest] = aTag.split(':');
+  const kind = Number(kindStr);
+  if (!Number.isFinite(kind) || !pubkey || rest.length === 0) return null;
+  return { kind, pubkey, identifier: rest.join(':') };
+}
+
+/**
+ * Is this kind-31871 event a *trade* attestation? We require a 30402 assertion
+ * (`a` tag) plus a counterparty (`p`) — our documented marker for trades.
+ */
+export function isTradeAttestation(ev: NostrEvent): boolean {
+  if (ev.kind !== TRADE_ATTESTATION_KIND) return false;
+  const a = ev.tags.find(([t]) => t === 'a')?.[1];
+  const coord = parseListingCoord(a);
+  if (!coord || coord.kind !== MARKETPLACE_ITEM_KIND) return false;
+  return ev.tags.some(([t]) => t === 'p');
+}
+
+/**
+ * Publish a trade attestation (kind 31871, addressable).
+ *
+ * `d` is derived from the listing + role so re-publishing the same attestation
+ * replaces it (e.g. to set `s=revoked`), per the NIP's lifecycle.
+ */
+export function useTradeAttestation() {
+  const { user } = useCurrentUser();
+  const { mutateAsync: publish, isPending } = useNostrPublish();
+
+  const publishTrade = async ({
+    listing,
+    role,
+    counterparty,
+    method,
+    amountSats,
+    state = 'valid',
+    note,
+  }: {
+    /** The listing being attested. */
+    listing: { pubkey: string; identifier: string };
+    role: TradeRole;
+    /** The other party's pubkey. */
+    counterparty: string;
+    method?: TradeMethod;
+    amountSats?: number;
+    state?: 'verifying' | 'valid' | 'revoked';
+    note?: string;
+  }) => {
+    if (!user) throw new Error('You must be logged in.');
+    if (counterparty === user.pubkey) throw new Error('Pick the other party, not yourself.');
+
+    const coord = `${MARKETPLACE_ITEM_KIND}:${listing.pubkey}:${listing.identifier}`;
+
+    const tags: string[][] = [
+      ['d', `${user.pubkey}:trade:${role}:${listing.identifier}`],
+      ['a', coord],
+      ['s', state],
+      ['p', counterparty],
+      ['alt', role === 'sold' ? 'SkateSpots: sale completed' : 'SkateSpots: purchase confirmed'],
+    ];
+    if (method) tags.push(['method', method]);
+    if (typeof amountSats === 'number' && amountSats > 0) {
+      tags.push(['amount', String(Math.round(amountSats)), 'SATS']);
+    }
+
+    const name = user.pubkey.slice(0, 8);
+    const content =
+      note?.trim() ||
+      (role === 'sold' ? `Sold by ${name}.` : `Bought from ${name}.`);
+
+    await publish({ kind: TRADE_ATTESTATION_KIND, content, tags });
+  };
+
+  return { publishTrade, isPending };
+}
+
+export interface TradeReputation {
+  /** Listings this pubkey sold (they attested as the listing author). */
+  sales: number;
+  /** Listings they attested as the non-owner party. */
+  purchases: number;
+  /** Deals where both sides attested the same listing. */
+  verified: number;
+  /** Distinct counterparties involved. */
+  counterparties: string[];
+  /** Raw trade attestations this pubkey is involved in. */
+  attestations: NostrEvent[];
+}
+
+/**
+ * Trade reputation for a pubkey: seller/buyer positions derived from kind-31871
+ * attestations, plus a "verified" count where seller and counterparty both
+ * attested the same listing (the strong, mutually-confirmed signal).
+ *
+ * NOTE: consumers should trust-weight counterparties with the existing WoT
+ * score so rings of fresh accounts can't inflate reputation.
+ */
+export function useTradeReputation(pubkey: string | undefined) {
+  const { nostr } = useNostr();
+
+  return useQuery<TradeReputation>({
+    queryKey: ['trade-reputation', pubkey],
+    enabled: !!pubkey,
+    staleTime: 5 * 60 * 1000,
+    queryFn: async (c): Promise<TradeReputation> => {
+      const empty: TradeReputation = { sales: 0, purchases: 0, verified: 0, counterparties: [], attestations: [] };
+      if (!pubkey) return empty;
+
+      const signal = AbortSignal.any([c.signal, AbortSignal.timeout(12000)]);
+      const events = await nostr.query(
+        [
+          { kinds: [TRADE_ATTESTATION_KIND], authors: [pubkey], limit: 200 },
+          { kinds: [TRADE_ATTESTATION_KIND], '#p': [pubkey], limit: 200 },
+        ],
+        { signal },
+      );
+
+      const unique = Array.from(new Map(events.map((e) => [e.id, e])).values()).filter(
+        (e) => isTradeAttestation(e) && e.tags.find(([t]) => t === 's')?.[1] !== 'revoked',
+      );
+
+      // Group by the attested listing coordinate.
+      const byListing = new Map<string, NostrEvent[]>();
+      for (const ev of unique) {
+        const coord = parseListingCoord(ev.tags.find(([t]) => t === 'a')?.[1]);
+        if (!coord) continue;
+        const key = `${coord.kind}:${coord.pubkey}:${coord.identifier}`;
+        const list = byListing.get(key) ?? [];
+        list.push(ev);
+        byListing.set(key, list);
+      }
+
+      const counterparties = new Set<string>();
+      let sales = 0;
+      let purchases = 0;
+      let verified = 0;
+
+      for (const [key, attestations] of byListing) {
+        const coord = parseListingCoord(key);
+        if (!coord) continue;
+        const seller = coord.pubkey;
+        const attestors = new Set(attestations.map((e) => e.pubkey));
+        const isVerified = attestors.has(seller) && attestors.size >= 2;
+        const involved = attestors.has(pubkey);
+
+        if (involved) {
+          if (pubkey === seller) sales++;
+          else purchases++;
+          if (isVerified) verified++;
+
+          // Record counterparties (everyone else who attested this listing).
+          for (const a of attestors) if (a !== pubkey) counterparties.add(a);
+          for (const ev of attestations) {
+            for (const [, value] of ev.tags.filter(([t]) => t === 'p')) {
+              if (value !== pubkey) counterparties.add(value);
+            }
+          }
+        }
+      }
+
+      return {
+        sales,
+        purchases,
+        verified,
+        counterparties: [...counterparties],
+        attestations: unique,
+      };
+    },
+  });
+}
+
+/**
+ * Trade attestations for one listing, from the viewer's perspective:
+ * `iConfirmed` (they attested it) and `counterparty` (who else has).
+ */
+export function useListingTrade(
+  listing: { pubkey: string; identifier: string } | undefined,
+  viewerPubkey: string | undefined,
+) {
+  const { nostr } = useNostr();
+  const coord = listing ? `${MARKETPLACE_ITEM_KIND}:${listing.pubkey}:${listing.identifier}` : undefined;
+
+  return useQuery({
+    queryKey: ['listing-trade', coord, viewerPubkey],
+    enabled: !!coord,
+    staleTime: 60 * 1000,
+    queryFn: async (c) => {
+      if (!coord) return { attestations: [] as NostrEvent[], iConfirmed: false, counterparties: [] as string[] };
+      const signal = AbortSignal.any([c.signal, AbortSignal.timeout(10000)]);
+      const events = await nostr.query(
+        [{ kinds: [TRADE_ATTESTATION_KIND], '#a': [coord], limit: 50 }],
+        { signal },
+      );
+      const attestations = events.filter(
+        (e) => isTradeAttestation(e) && e.tags.find(([t]) => t === 's')?.[1] !== 'revoked',
+      );
+      const authorSet = new Set(attestations.map((e) => e.pubkey));
+      const counterparties = new Set<string>();
+      for (const ev of attestations) {
+        for (const [, value] of ev.tags.filter(([t]) => t === 'p')) {
+          if (value !== viewerPubkey) counterparties.add(value);
+        }
+      }
+      for (const a of authorSet) if (a !== viewerPubkey) counterparties.add(a);
+      return {
+        attestations,
+        iConfirmed: !!viewerPubkey && authorSet.has(viewerPubkey),
+        counterparties: [...counterparties],
+      };
+    },
+  });
+}

src/pages/NIP19Page.tsx

@@ -10,6 +10,7 @@ import { Badge } from '@/components/ui/badge';
 import { Skeleton } from '@/components/ui/skeleton';
 import { ZapButton } from '@/components/ZapButton';
 import { ZapBadgesCard } from '@/components/ZapBadgesCard';
+import { TradeReputationCard } from '@/components/TradeReputationCard';
 import { ClinkPayButton } from '@/components/ClinkPayButton';
 import { useAuthor } from '@/hooks/useAuthor';
 import { useCurrentUser } from '@/hooks/useCurrentUser';
@@ -712,6 +713,9 @@ function ProfilePage({ pubkey }: { pubkey: string }) {
             {/* Zap achievements (only renders when this profile has sent zaps) */}
             <ZapBadgesCard pubkey={pubkey} />
 
+            {/* Marketplace trade reputation (only renders with trades) */}
+            <TradeReputationCard pubkey={pubkey} />
+
             {/* Quick Info Card */}
             <Card className="bg-black/90 border-2 border-gray-800">
               <CardHeader className="pb-3">